Electronically tunable, high repetition rate (>10 GHz) mode-locked semiconductor lasers can be viewed as an optical counterpart of the voltage controlled oscillators (VCOs) in electronic circuits, which are of fundamental importance for controlled high speed logic and digital communications. The research for such monolithically integrated mode-locked semiconductor lasers has been extensive ever since its onset about 15 years ago. In most cases, a short, reverse biased active section is used for saturable absorption. The use of ion implantation to form a saturable absorber was also investigated. These schemes involve more processing steps than ordinary laser diode fabrication. Self-mode-locked semiconductor lasers based on Kerr lens mode locking have been reported in quantum cascade lasers that utilizes intersubband electron transitions, which have large and ultrafast optical nonlinearities (see for example, the article by R. Paiella, F. Capasso, C. Gmachl, D. L. Sivco, J. N. Baillargeon, A. L. Hutchinson, A. Y. Cho, and H. C. Liu, “Self-mode-locking of quantum cascade lasers with giant ultrafast optical nonlinearities,” Science, 290, 1739-1742 (2000)). This scheme may not need additional processing steps in fabrication and therefore is preferred. However, the inherent self-mode-locking effect in semiconductor lasers at 1.55 μm, which involves interband transitions rather than intersubband transitions, is much weaker. Recently, enhancement of weak self-mode-locking using picosecond-pulse injection has been reported in broad-area semiconductor lasers. What is needed is an improved self-mode-locked (SML) semiconductor laser that does not require additional processing steps in fabrication.